On a PC computer equiped with Windows 2000, I had a major problem of network slowness (when accessing the network, all operations seemed to atke ages to complete). I admit I was somewhat lost without a solution. So, I decided to use the ever-powerful solution: Google. It allowed me to find a web site with a very deeply documented page specially built to solve problems of slow network on Windows. The page contains everything you shoudl check and solutions to a lot of cases. And there is a lot of choice!
Thus, I was quickly stopped by a remark about the use of several network cards on the same machine. And my mind suddenly lit like a candle! It happens that this problematic PC has no less than 3 network interfaces including an unconnected one. So, it was only a matter of checking -as advised- that they were all disabled (except a single one) to get a proper operation back in seconds.